The present invention relates to a slide closure for metallurgical vessels, in particular steel pouring vessels of the type including a housing attached to the bottom of the vessel and positioning therein a refractory apertured fixed plate, possibly by means of a metallic holding frame, the housing also having positioned therein a metallic slide which carries a refractory apertured slide plate. The slide is displaceably supported by means of sliding surfaces on rails of a housing cover which closes the bottom of the housing.
As is well known, slide closures of the above-mentioned type are employed for opening, throttling and closing the spout of metallurgical vessels. The slide plate with a passage therethrough is displaced with respect to a passage extending through the fixed plate arranged above the slide plate. The two refractory plates, together with the inlet and outlet sleeves of the closure, are subjected to unusually high thermal, chemcial and mechanical stresses, particularly in the vicinity of the through-flow passages. In addition to an unsatisfactorily short useful life, which in the case of a steel pouring operation frequently lasts only for a single emptying of the vessel, the stresses cause difficulties with regard to operational reliability and saftey of the vessel.
Considerable efforts have been exerted to counteract these disadvantages. Thus, the refractory material of the plates has been improved. Especially with regard to steel melts, plates carefully produced, e.g. from highly aluminiferous material are particularly resistant to thermal and chemical stresses. On the other hand, until the present time it has not been possible to avoid destruction of the plates due more or less to mechanical stresses.
Protracted observations allow the assumption that the mechanical stresses which destroy the fixed plate and the slide plate result from the unavoidably differential thermal expansion of the two plates during the pouring operation, since the plates in the areas of the passages therethrough are subjected to considerably higher expansion due to the higher temperatures prevailing in such areas than at the edges of the plates. Accordingly, the plates each tend to develop a convex curvature. This unavoidable expansion increases the tendency of reciprocal clamping or locking between the fixed plate holding frame and the slide plate carrying slide in the slide housing. This clamping provides for a leakage free sailing between the two reciprocally contacting sliding surfaces of the plates. In addition to the above-mentioned thermal and chemical stresses, high local compressive stresses occur in the areas of the passages of the plates owing to the expansion of the plates, and also due to the above-mentioned clamping or locking of the plates. These compressive stresses exert a decisive negative effect on the useful life of the plates, and by jamming the plates endanger the operational capacity and reliability of the slide closure.
This relationship between local expansion and locking, as well as their effects, was not known until the present time. Among men skilled in the art, there prevailed the uniform opinion that the elimination of leakage in the closure, which is absolutely required for reliable operation, could be achieved only through the provision of maximum rigidity in the structure of the slide and of the fixed plate holding frame in the area of the passages through the plates.
Known systems for preliminary tensioning or prestressing of the fixed plate and the slide plate in the slide housing, effected by means of the housing cover with the interposition of springs, exclusively take into account the general thermal expansion of the parts of the slide closure, but do not take into account the differential thermal expansion of the plates, which has been recognized as being a decisive importance.